This invention relates to continuous power systems. In particular, the present invention relates to continuous power systems that utilize a source of stored thermal energy to provide a continuous supply of electric power when a primary power supply fails, or when deterioration occurs in the power being supplied to the end user.
Continuous power systems are often used to insure that, when a primary power supply fails due to equipment malfunction, downed lines or other reasons, electric power will continue to be supplied to critical loads such as telecommunication systems, because, for example, telecommunication systems often include facilities that may be in relatively isolated locations, such as a telecommunication repeater tower. Other applications of the present invention include hospital operating room equipment, computer systems and computerized manufacturing equipment. Continuous power systems avoid equipment failures, costly downtime and equipment damage.
Known continuous power systems may employ an uninterruptible power supply (UPS) to provide alternating current (AC) power to the end user or critical load, or may use other electronic means to provide DC power to the end user or critical load.
For known continuous power systems, batteries or flywheels may be employed as energy storage subsystems to provide bridging energy while a fuel-burning engine is started. Such flywheel systems may include a flywheel connected to an electrical machine that can operate both as a motor and a generator. For example, U.S. Pat. No. 5,731,645 describes flywheel systems that provide backup power to the load in UPS systems. The electrical machine is powered by a DC buss to operate as a motor when acceptable power is received from the primary power supply. When power from the primary power supply fails (or is degraded), the electrical machine is rotated by the kinetic energy of the flywheel and operates as a generator to supply power to the DC buss.
Continuous power systems often use prime movers (e.g., fuel-burning engines) to drive backup generators during prolonged power outages. These prime movers, however, are often costly, complicated, and may require extensive ongoing maintenance. In addition, the engines themselves may fail to start, resulting in a loss of power to the critical load. Moreover, some localities limit the running time or the number of starts per year for backup generator engines, thereby limiting the ability to test and maintain such systems.
Other energy storage systems currently used to provide backup power are often expensive and complicated. For example, in typical battery energy storage systems, there is a risk that undetected battery damage or corrosion of battery terminals can result in a failure to deliver backup power when needed. Moreover, batteries have a limited shelf life, in addition to requiring expensive ventilation, drainage, air conditioning and frequent maintenance. Flywheel energy storage systems, while avoiding most of the disadvantages of batteries, can be expensive since they are often mechanically complex and can require complicated power electronics.
Some known systems provide long-term power by driving a shaft-mounted generator with a turbine. For example, U.S. Pat. No. 6,255,743 describes an uninterruptible power supply system that includes a shaft-mounted generator and a turbine. These turbines may be open systems, where the turbine is driven by a fuel source that is regularly renewed, such as LP gas, methane, gasoline, diesel fuel. In such instances, the turbine exhaust is allowed to escape into the environment.
Typical turbine-based systems, however, often rely on many individual components that are assembled together to form the complete system. This may result in potential problems in interconnecting the components together, such as cooling and power distribution within the system. In addition, there may be a reduction in overall system efficiency and/or reliability if, for example, multiple shaft-mounted devices are each installed on their own shafts and the shafts are then coupled together by some form of linking mechanism.
The use of a turbine in a continuous power supply system may create additional problems. For example, the design and manufacturing of the turbine nozzle may be particularly important because of the need to inject a potentially limited quantity of vapor into the turbine and still drive the turbine with enough force that the spinning turbine can drive a generator fast enough to produce high quality power. This may require special tooling or other special manufacturing processes which can significantly increase the cost of manufacturing the system.
Accordingly, it is an object of the present invention to provide continuous power system assemblies that utilize integrated components.
It is another object of the present invention to provide continuous power system assemblies that utilize a common cooling system.
It is a further object of the present invention to provide continuous power system assemblies that are configured to enable relatively simple installation and maintenance.
It is a still further object of the present invention to provide continuous power system assemblies for turbine systems that include high efficiency nozzles, that can be manufactured economically.
The continuous power system assemblies of the present invention provide numerous advantages by integrating several components of the assembly into a single housing. One of the advantages of such a configuration is the improved ease of installation over conventional systems, which is particularly applicable when the continuous power systems are installed in remote locations, such as in a telecommunications site. The assemblies of the present invention include an integrated unit that contains a turbine, an alternator, a pump and a flywheel, all mounted to a single shaft in a common housing.
The turbine may be used to provide shaft-driving force during both SHORT-TERM and LONG-TERM OUTAGES of the primary power source (e.g., utility power). It should be noted that an OUTAGE, as defined herein, includes both an interruption in power from a source (such as utility power), as well as a degradation in quality of the power delivered by the source. During a SHORT-TERM OUTAGE, a source of stored thermal energy may be used to vaporize working fluid to drive the turbine. During a LONG-TERM OUTAGE, a gas-fired burner, for example, may be used to vaporize the working fluid used to drive the turbine. In that case, the turbine would continue to drive the continuous power system until utility power was restored or the fuel supplied to the burner was exhausted.
Another source of energy that may be used to drive the shaft comes in the form of kinetic energy stored by the flywheel, which is rotated at a given speed by utility power during STAND-BY mode. During a SHORT-TERM OUTAGE, the flywheel, instead of or in addition to the source of stored thermal energy, provides the force used to drive the shaft. The use of either or both sources of back-up power may depend on the specific circumstances of a given OUTAGExe2x80x94one or both sources may be used to provide bridging energy until the gas-fired burner is fully operational. It is preferable to utilize the stored kinetic energy first, as it is instantly available while the thermal energy is available only after a brief delay.
During STAND-BY mode, the continuous power systems of the present invention provide utility power to the alternator (which may be a single electrical machine that is operable as both a motor and as a generator), which acts as a motor and drives the common shaft. The rotation of the shaft causes the flywheel to be spun up to its STAND-BY speed, so that it stores a given amount of kinetic energy. During all other modes of operation, the shaft is driven by another source of power and the alternator operates as a generator that provides the necessary back-up power.
An additional feature of the present invention is the inclusion of a feed pump in the integrated unit. The feed pump, which is also mounted to and driven by the common shaft pressurizes the working liquid fluid so that it can be re-vaporized and superheated. In this manner, the energy from the turbine itself is used to replenish the supply of working fluid to the turbine. For example, in a closed turbine system, the feed pump may be used to pump condensed working liquid (i.e., the exhaust of the turbine that was condensed back to liquid) to an evaporator that converts it back to liquid for injection into the turbine.
The turbine, which may be mounted at one end of the assembly, includes nozzles that direct superheated working vapor onto the turbine wheel. The nozzles, in accordance with the present invention, are configured in a convergent/divergent design, similar to a Venturi, so that the vapor is accelerating as it is injected into the turbine. This results, however, in a very narrow nozzle throat width. The nozzle block containing the nozzles, which is described in more detail below, is constructed in accordance with the principles of the present invention by placing half of the nozzles on two halves of a nozzle block which is then mated together. This permits the nozzle throats to be machined inexpensively without any special tooling, and also permits the nozzle block halves to be cast, which further reduces manufacturing costs.